Gasket and gasket composition



-' vacuum brake assemblies.

' his foot.

yatented June 14, 1949 man o STATES orFicE GASKET AND GASKET COMPOSITIONHerbert A. Winkelmann, Chicago, Ill., assignor to Dryden Rubber Company,Chicago, 111., a corporation oflllinois No Drawing. Application November10, 1947, Serial No. 785,183

4 Claims. (01. 260-19) The invention relates to a gasket and gasketcomposition particularly adapted for use in the vacuum brake assembly ofan automobile.

Leather gaskets having a wick containing a lubricant to prevent thesticking of the gasket to the cylinder walls are commonly used in theseHowever, due to the high price of leather attempts have been made tomake these gaskets out of synthetic rubber, but hitherto all attemptshave failed because the compositions stuck or froze to the cylinderwalls. It was found, for example, that after a truck stood over night itrequired more pressure to remove the piston of the brake mechanism thana man could exert by pressing as hard as he could with An object of thisinvention is to provide a synthetic rubber gasketwhich will notfreeze'to the cylinder walls even when used without a wick.

Another object is to provide a suitable gasket for a vacuum brakeassembly which is less expensive than a leather gasket.

A further object is to provide a self-lubricating gasket composition.

Other objects will become apparent from the following specification.

In accordance with this invention, the following ingredients inproportions as stated are mixed together: Butadiene-acrylonitrilecopolymer synthetic rubber containing 20 to 55 by wei ht ofacrylonitrile, preferably from 40 to 45% of acrylonitrile, the remainingbeing at least 90% by weight butadiene-25 to 65% by weight of thecomposition, preferably 30% to 40% by weight ofthe composition.

A liquid petroleum oil, at least 90% by weight,

having a boiling point at least 150 above centigrade, and at least 75%consisting of aliphatic hydrocarbons25 to 60, preferably 35 to 50 partsby weighton 100 parts by weight of copolymer.

Graphite-10 to 125, preferably 10 to 25 parts by weight on 100 parts byweight of copolymer. A thermosetting phenol formaldehyde resin,preferably a solid-phenol formaldehyde resin of the type sold by DurezPlastics 8: Chemical, Inc.

under the name of Durez 12687--10 to 75, preferablyiO to 35 parts byweight on 100 parts by weight of copolymer. I

Sulfur-1 to parts by weight on 100 parts by weight of copolymer.

vulcanization accelerator such as mercaptobenzothiazyl-disulfide-J, to5, preferably 1 to 2 parts by weight on 100 parts by weight ofcopolymer.

Rubber antioxidant such as phenyl-beta-na-phthylamine-O to 5, preferably0.5 to 2 parts by weight on 100 parts by weight of copolymer.

Carbon black-0 to 125, preferably to 125 parts by weight on 100 parts byweight of copolymer.

Paraifin-O to 5,'preferably 1 to 4 parts by weight on 100 parts byweight of copolymer.

Stearic acid-0 to 2, preferably .2 to 1 parts by weight on 100 parts byweight of copolymer.

Zinc oxide-0 to 10 parts by weight on 100 parts by weight of copolymer.

Ester 'plasticizer. compatible with the copolymer such as tributoxyethyl phosphate, tricresyl phosphate, dioctyl phthalate, dibutylsebacate, dibutyl phthalate, dibe'nzyl sebacate-O to 30, preferably 10to 30 parts by weight on 100 parts by weight of copolymer.

It is apparent from the above that the most important ingredients arebutadiene-acrylonitrile copolymer synthetic rubbers, petroleum oil,graphite, phenol formaldehyde resin, and vulcanizing agent. The graphiteis particularly im portant in giving desirable slip and should not bedecreased below 10 parts per 100 parts of the butadiene-acrylonitrilecopolymer. The petroleum oil likewise is useful for imparting slip andalso forgiving a self-lubricating effect. The phenol formaldehyde resinim arts slip and aids in obtaining high gloss. The three ingredients,graphite, oil and phenol formaldehyde resin, act together to give thedesirable characteristics, and it has been found that no one of thesecan be eliminated without detrimental effect.

For some purposes where hardness is not important, it has been foundthat polyvinyl chloride resins may be substituted for the phenolformaldehyde resins, particularly blends of polyvinyl chloride andbutadiene-acrylonitrile synthetic rubber. v I

Use of carbon black aids in obtaining slip. Where carbon black is usedless phenol formaldehyde resin is necessary to give the desirable slipcharacteristics.

The type of butadiene-acrylonitrile synthetic rubber is important. Ingeneral the acrylonitrilo content of the copolymer should not besubstantially less than 20% by weight of the copolymer.

Ester plasticizers may be used with the copolymer to increaseflexibility. Tributoxyethyl phos- 3 ic rubber, and suitably may be at atemperature from 2'75 to 320 1''. for a period of time from 10 to 30minutes depending upon the thickness.

The gasket made from my composition is characterized in that it has nodrag and ieels smooth and slippery. The use of a polished and chromeplated mold enhances the smoothness. me gasket has a further advantageof being oil resistant. It is self-lubricating due to exudation andsweating out of the petroleum oil which is only partially compatiblewith the coDoLvmer.

The following are examples of some specific compositions which havegiven satisfactory resuits:

Example No.

But dieue-acrylonitrlle copolymer of 45% ecrylonimo tr eButgdleue-acrylonitrile copolymer oi 30% acrylcnino tr eButadieue-acrylonitrllc copolymer of 26% lcrylonim tr e. Castor (carbonblack) 110 110 110 Graph 15 lb 16 Durer 12687 (phenol formaldehyderesin) 20 2o 16 Siearlc a 0. 5 0. 5 0. 6 Sulfur 1.6 1.5 l. 5 Altar(mercaptobenzothlml disuifldc) 1.5 1.5 1.5 mo 4. a z s a ll l bet hth 1l g i 1 env a-nap y am no 'lribuioxyethyl phosphate. ["15 15 Petroleumoil 45 Q 45 45 Tensile p. s 855 095 876 Percent on 225 210 290Modulus@200% 830 935 740 Lbs. 'lear 186 146 145 Hardness 74 75 While Ihave described certain preferred embodiments of my invention, manymodifications thereof may be made without departing from the spirit ofthe invention; and I do not wish to be limited to the detailed examples,formulas and proportions of ingredients herein set forth. but desire toavail myself of all changes within the scope of the appended claims Iclaim:

1. A gasket composition comprising from 25% to 65% by weight of abutadiene-acrylonitrile copolymer synthetic rubber containingacrylonitrile in an amount not less than by weight of the copolymer, aliquid petroleum oil at least 90% by weight having a boiling point of atleast 150 C. and at least 75% consisting of aliphatic hydrocarbons, saidpetroleum-oil being present in an amount from to 60 parts by weight on100 parts by weight of said copolymer, graphite in amount from 10 to 125parts by weight on 100 parts by weight of said copolymer, athermosetting phenol formaldehyde resin in amount from 10 to parts byweight on 100 parts by weight of said copolymer, and suiiur from 1 to 5parts by weight on 100 parts by weightoi said copolymer.

2. A gasket composition comprising 30% to by weight of abutadiene-acrylonitrile copolymer synthetic rubber containing 20% to ofacrylonitrile, a liquid petroleum oil at least 90% by weight having aboiling point of at least 150 C.

and at least consisting of aliphatic hydrocarbons, said petroleum oilbeing present in an amount from 35 to 50 parts by weight on 100 parts byweight of copolymer, carbon black in an amount from 50 to 125 parts byweight on 100 parts by weight on parts by weight of copoly- 7 mar,graphite 10 to 25 parts by weight on 100 parts by weight of copolymer,paraflin 1 to 4 parts by weight on 100 parts by weight of copoly-' mer,stearic acid .2 to 1 parts by weight on 100 parts by weight ofcopolymer, an ester plasticizer compatible with said copolymer in anamount from 10 to 30 parts by weight on 100 parts by weight ofcopolymer. 3. A gasket consisting of a body in the form of a ring havingthe vulcanized composition of claim 1.

4. A gasket consisting of a body in the form of a ring having thevulcanized composition of claim 2.

HERBERT A. REFERENCES men The following references are of record in thetile of this patent:

UNITED STATES ra'rnu'rs Number Name Date 2,358,290 Kraft Sept. 12, 19442,373,461 Crampton Apr. 10, 1945 Patent No. 2,473,319.

Certificate of Correction June 14,1949.

HERBERT A. WINKELMANN It is hereby certified that errors appear in theprinted specification of the above numbered patent requiring correct-ionas follows: Y

Column 4, line 20, claim 2, for thermostettingf read thermosetting;line25, same "claim, for accelerated read dccelemtor;

andthat the said Letters Patent should beread with these correctionstherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 8th day of l lovember, A. D. 1949.

THOMAS F. MURPHY, Assistant Oommz'm'oner of Patents.

